1. Technical Field
The disclosure relates generally to ion implantation, and more particularly, to a cathode having electron production and focusing grooves for an ion source of an ion implanter, the ion source and a related method.
2. Background Art
A cathode and a repeller are positioned within an ion source of an ion implanter to generate an ion plasma by injecting electrons into a source gas. The repeller is at the same potential as the cathode but is not heated—its purpose is to prevent electrons escaping the plasma by reflecting them back into the plasma. When installed, the cathode and repeller both present a substantially planar working surface to the source gas. However, as the ion source is used, their working surfaces erode to have a concave surface, especially that of the cathode. The concave surface acts to increase the output of the ion source, particularly as the cathode approaches the end of its useful life. In particular, the concave surface of the cathode focuses the thermionic electrons in a central region of the plasma, which increases output. Unfortunately, the duration of the increased output is limited due to the cathode reaching the end of its useful life.
One approach to take advantage of the increased output is to build a cathode having a concave surface. This approach, however, is not tenable for a number of reasons. First, the concave surface cathode may reduce the lifetime of the cathode due to the thinner center. Typically, failure occurs at the center of the cathode. Furthermore, the concave surface cathode may require structure that presents a higher thermal mass, which is difficult to heat and control, e.g., if the edges of the cathode surface are thicker.